The invention relates to a radial fanwheel with a hub and a plurality of fan blades, the blades being in an array that is disposed concentrically with respect to the hub and forwardly bowed (i.e., curved as if bent forwardly at its ends so as to form a forwardly open concave surface), the blades being linked to the hub by spokes.
Radial fanwheels of the type described above, also known as drum fanwheels, are used for single-flow blowers, i.e., blowers with a unilateral intake; or for double-flow blowers, i.e., blowers with a bilateral intake. It is known that the fan blades can be mounted to the hub by means of a disk, whereby the tips of the fan blades are held by rings or cover disks. When the disk, which serves as a connecting part, is connected with one of the two cover disks, the fanwheel is limited to a single-flow blower design. It is also possible to attach the connecting disk to the fan blades between the two covered disks, producing a radial fanwheel suitable for a double-flow blower. The arrangement of the disk determines the flow distribution, i.e., the air volume to be drawn in from one side or the other. If a different distribution is desired, another radial fanwheel with a suitably different arrangement of the connecting disk must be manufactured.
Radial fanwheels of this type are also oriented rotational-directionwise. Their asymmetrical design makes it impossible to convert them to a different rotational direction simply by turning them through 180.degree.. Instead, different radial fanwheels must be manufactured for clockwise rotation and for counterclockwise rotation. These measures result in a considerable manufacturing cost increase and in costly stock maintenance.
It has also been proposed (German Patent Application No. P 29 39 385.9-15) to provide the connecting disk with apertures, so that, in effect, the fan blades are linked to the hub by spokes. This design has the advantage of producing a radial fanwheel which can be used as both a single-flow blower and a double-flow blower, since the air volumes drawn in are automatically distributed through the openings. In this design also, however, at least two different radial fanwheels must be manufactured to permit one arrangement with clockwise rotation and another arrangement with counterclockwise rotation, resulting in high manufacturing costs.
Thus, a principal object of the present invention is to achieve a radial fanwheel of the type described above that can be used either for a single-flow or a double-flow blower, with clockwise or counterclockwise rotation, independently of the intake direction. This object is attained in a preferred embodiment by virtue of the fact that backwardly-curved spokes are staggered with respect to one another and arranged successively around the circumference relative to the radial center plane, each of said spokes holding a fan blade in the vicinity of one of its ends in such a manner that each fan blade is connected at one end with the fan blade ahead of it in the circumferential direction and at the other end with the fan blade behind it.
This design makes it possible to devise a radial fanwheel whose structure is symmetrical with respect to the radial center plane, so that it can be used for either clockwise or counterclockwise rotation by simply turning it through 180.degree.. It is also possible to use this radial fanwheel in either single-flow or double-flow blowers, since the spokes do not significantly impede the air flow and thereby permit free air distribution. An endless meander-shaped structure composed of fan blades and running in the circumferential direction of the radial fanwheel is conceptually part of this invention. Furthermore, this structure is manufacturable as a plastic part by using an injection molding machine, especially since no rings or cover disks are provided for the fan blades. In this regard, it is noted that the curved shape of the blades is produced by the shape of the mold cavity so that, while the term "bowed" is used relative to blades produced in such a manner, it should be understood to mean only that they are in the shape of a simple curve and not that the blades are actually "bent" from a straight configuration.
In order to produce a radial fanwheel of this type while designing the invention so that it is capable of adjusting automatically to different load conditions and forces which develop, especially in conjunction with a drive motor which changes its rotational speed as a function of load, a provision is made for the spokes and fan blades and/or the connecting elements linking the fan blades to be so dimensioned that the radial length of the spokes can change by elastic modification of the curvature of the spokes, and the diameter of the blade ring formed by the fan blades can be modified by elastic twisting and/or bending of the fan blades and/or of the connectors, depending on the loads which develop.
A radial fanwheel in accordance with the present invention has, firstly, the advantage that balancing is no longer required, since any slight imbalance which might possibly be present as a result of the injection molding technique will cause the radial fanwheel to deform slightly elastically during operation to conform to this imbalance, so that it runs smoothly after this deformation has taken place. There is no feedback of the imbalance through the elastic spokes, so that no balancing measures need be taken. A fanwheel of this type also has the advantage that it adapts to a certain extent to load conditions as they change, and serves to offset them. For example, if the load increases, the aerodynamic forces acting circumferentially on the fan blades cause the spokes (which are curved oppositely relative to the forwardly bowed blades) to flex, thereby reducing the diameter of the blade ring. In the case of the drive motor which changes its rotational speed as a function of load, a similar diameter reduction occurs when a reduction of the rpm reduces the centrifugal forces which stretch the spokes and expand the blade ring. In the opposite case, when the load decreases, the spokes stretch and increase the blade ring diameter in such fashion that the effect of the aerodynamic forces is less and the effect of the centrifugal force is greater.
In an advantageous embodiment, provision is made for the spokes, fan blades, and connecting elements to be so designed and/or dimensioned that, in the event of load-dependent deformation, essentially constant blade geometry is maintained. This measure ensures that the entry and exit angles of the fan blades likewise change as a function of load, and adjust themselves to the changed load. When the load decreases, the entrance and exit angles increase; they decrease when the load increases.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.